Telephone-exchange system.



PATENTED MAY 14, 1907.

A. R. KAHL. TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED JAN. 31, 1906.

2 SHEETS-SHEET l,

lhveniur ltmr Kahi VVIFTEEEEE: @325 ZK fi w W ATIGPFLELL PATENTED MAYM, 1907.

A. R. KAHL. TELEPHONE EXCHANGE SYSTEM.

APPLICATION FILED JAN.31, 1906.

2 SHEETS-SHEET 2.

UNITED STATES ARTHUR n. KAHL, O ROCHESTER, NEwYoRK, ASSIGNOR 'r'o STROMBERG- MANUFACTURING COMPANY, or ROCHESTER,

)AR'LSON TELEPHONE PATENT orricn NEW YORK, A CORPORATION OF NEW YORK.

TELEPHONE-EXCHANGE SYSTEM.

Specification of Letters Patent.

Patented May .14, 1907,,

' Application filed January 31, 1906. Serial No. 2 98, 741.

To all whom it may cor warn;

Be it known. that I, Anrnun R. KAHL, a

citizen of the-,United States, residing at Rochester, in the county of Monroe and a full, clear, concise, and exact description,

reference being had to-the accompanying;

drawings, forming a part of this specification. My invention .relatesto telephone ex:

change systems, particularly to automatic selective ringing arrangements.therein.

of this kindit is usual to em- In systems ploy a plurality of selective ringing keys connected with selective signaling current sources, locking means'being also provided for the keys and controlled by locking relay mechanism, and other relay mechanisms are employed. acting in COIIJUIlCtIOIl with the locking relay mechanism,

matically maintain connection of the ringing current with the calledline and to auto-. matically disconnect the ringing current when the called subscriber has answered.

It is the object oi' my'invention to provide improvedrelations and arrangements forand. the details ofmy invention will be best these various automatic mechanisms,

understood reference to. the accompanying drawings", in which 7 Figure diagrammatically illustrates the arrangements and relations oi the parts.-

Fig. 2 illustrates the mechanical embodiment" of the various selective keys and controlling magnet therefor. on line 3-3 of Fi 2.1 .Fig. 4 is-an end view of the key-shown in members of pulsating mechanism.

In Fig. 1 is shown the substation A con-;

nected by line limbs a, b with-the central- .exchange, these line limbs being continuous normal 7 through armatures, 1 and 20f the cut off relay. 3 and including the windings 4 and 5 of the indicator relay fijconnecting then with the terminals of the common source of current At the substation is' provided the usual telephonicapparatus comprising a switch, hook' 7',- receiver 8,

transmitter 9', si' 1 1. The multip e a spnngj acks '12 and. 13. are

and keys" to auto lamp 29. The supervisory relayior the Fig. 3 is. a sectional view 1 Fig. 2,- and Figs. 5 and '6 diagrammatically illustrate the relation of '5 by the bells 10 arid condensertest thimbles 14 and 15 thereof are connected together by conductor 16 which includes the cutoff relay 3 and terminates at the positive poleof battery S. Line signal-17 is controlled by thelrelay 6; ThefsubstationB is provided with similar apparatus as substation A, and connects through the line limbs with the central exchange, the cut-eff relay mechanism and the connections there; for being the same as those connected with the substation A. The reference characters of the substationtelephonic apparatus, line and central station apparatus are primed, I

however. This line is-shown as a-party line, and. besides the substation B are shown the substations B B and'B 4 The cord circuit at the central exchange terminates in the callin lug 19.1 included in th tip strandsof the cord circuit, respectively, answering and the calling sides thereof. The

supervisory relay for the answering: side is of the compound type c0mprisinglW1ndings-22' and 23. v The armature 24 of t e winding 22 is mechanlcallyconnected-with the spring 25, whose tendency is to engage with the contact 26 but prevented from oing so by the action of .the spring 27' engaging the armature 28 for the winding 23. The contacts and 26 are in'circuit with the. supervisoily ca 1- ing side comprises windings 30 and'31. The armature 32 for the winding30is mechanic'- ally connected with the spring. 3 3, whose tend- ,fency is to connect with the contact 34 but prevented from doing so the force of the sprin' 35* connected withfithe armature 36 for t e winding 31.

This armature 36 is mechamcally connected with the contact 37 which normally engages the con-- tact 38-;and'upon energization0f the win-ding being -engaged with contact. 39. The contacts 33'a'nd 34 control.the-circuitthrough the supervisory'l-amp 40.

The connection withthe line ofthe operators telephonic apparatus 0 is controlled osition-of t e ke'y springs 41 and 42,

this t'e'ephonic apparatus being connected with the alternate contacts 43 and 4:4. The

selective automatic ringing apparatus comprises the keys 45, 45 45 and 45 with which are associated to conductively separate the the sources-46 46 46 answering plug 18 andthe' Condensers 20 and-21 are correspondin of selective ringing current. The actuating springs47 47 47 and 47 are connected together with the alternate contact 48 of the relay 49. The actuating springs 50 50 50 and 50 are connected together with one terminal of therelay 51, Whose other terminal connects through conductor 52 with the negative side of the common battery. The alternate contacts 53, 53", 53 and 5 3 ofthe springs 50, 50 50 and 50 are connected together and through conductor 54 with the supervisory contact 337 The alternate contacts 55 55 55 and'55 for-the actuating s rings 47, 47 ,47 -and 47 are connected t rough interrupters 56 56 56 and 56 with one terminal of one of the signaling generators, whose other terminals are connected with the conductor 57 terminating in the alternate contact 58 of the relay 49. An auxiliary interrupter 59 is associated with these other interru ters, being mounted on a common shaft therewith. Each of the in.ter

rupters 56 56 56 and 56 comprises a ring '60 all connected to the groun ed conductor 61 and with'the contact ring 62 of the interrupter 59, the rin 63 of the int-errupters being connected wit the generators, as before stated. A third ring comprisin segments 64 and 65 is also provided for eac interru ter, the segment 64 being connected withthb ringl and the segment being connected wit the ring 68, this segmentl65 being the part of the interrupter connected with the and 55 for the selective key. ring comprising the insulated segments 66 and 67 is provi ed for interru ter 59,'the se ment-66 being connected wit ring 62 and t us with ground, while the segment '67 connects through conductor 68 with the contact 69 for the relay 5-11 This relay 51 is the locking relay and its mechanical association with the.

selective keys is best shown in Figs. 2, 3 and 4, the reference characters in these figures applied to the various switch springs and contacts-corresponding to those shown in the dl'agrammatlc view 111 Flg. 1.

The locking various. elecrelay, besides controlling the is mechanically assotrical connections,

ciated with the locking bar orv plate 7 0, this provided with the openings 71;

plate bein through w%.ich may ass the cams 7 2 carried on the stems 73 of t e actuating buttons 74, the arrangement being such that upon'depression of a key and subse uent lateralmovement of'the plate the epressed key Wlll be locked in its depressed position until the relay 51 becomes de'einergizedl. This relay controls the armatures or springs 75 and 76, the springs 75 being connected with one terminal ofthe relay 49, whose othefterminal connects through conductors 77 and 78 With the negative side of the common battery. The armature or spring 76 of relay 51 normally engages its contact 76 to close the alternate contact 55 55 55 sleeve strand of the calling side of thecord circuit, which sleeve strand is' also in contact 7 with armature 79 of the relay 49.

The other armature 80 of this relay connects with the tip strand of the calling side of the 'cord circuit and the cont act 8]. for this-armatureconnects with the supervisory relay sprlng 37 Having thus describedi'n general the varidesired. Immediately upon connection of' the cord circuit with the calling line the following circuit is closed:' negative side of battery S, conductor 78, conductor 82, supervisory winding 23 to the sleeve strand of the answering side through the plug sleeve contact and pack thimble,,throughconductor 16 and through the cut off relay 3 to the posi-' tive side of the battery. The cut. off relay, becoming ener ized, disconnects the relay from circuit an the indicatinglamp 17 is extinguished. Current flow through the winding 23 causes attraction ofthe armature 28 which normallywill have a tendency to allow spring 25 to engage contact 26'to cause illumination of the supervisory lamp 29 throu h the, circuit leading from negative sidefo battery through supervisory lamp 29,

contacts 25 and 26 and conductors 83 and,84 "to positive' side of battery.- Circuit, however, is also closed through winding 22 of the supervisory relay through the following path: negative side of-battery S, conductor 78, windlng 23, sleeve strand and contact through the springjack to line .limb by through the telephonic apparatus at thesubstation back through limb a, through the springjack to the tip contact and strandof the cord circuit, through conductor 84, windin 22 and conductors 83 and 84 to positive sid e of battery, the armature 24 being then attracted to prevent engagement of contacts 25 and 26', thus preventing illumination of thesupervisory lamp 29. Supposin the operator inserts the calling plug 19 into the spring-jack, therebycausing closure of acircuit on the negative side of batteryS through-conductor 78, conductor 85, winding 31' of the supervisory relay, through conductor 86, through sleevestrand and contact on the calling side of the plug circuit, through the engaged jack th'mble to the corresponding eut-ofi relay back to posithat the desired connection were with substation. B,

'tive side of battery; The armature 36 being attracted carries the sprin 37 into engagement with contact-39 and alows spring 33 to engage contact 34 whereby the supervisory -lamp 40 is illuminatedthrough the following tor'now actuates the corresponding key which is connected with the source 46 which supplies signaling current to which the bell at 53 conductor 54, contacts 33 and 34 of the supervisory relay and conductors 86' and 84 back-to battery. Ener 'zation of the relay 51 d of the calling sidelofi t e' cord circuit, while'the armature 75 engages the contact 69 to connect the interrupter 59 with therelay 4 9. ment' of'the actuating spring 47."-

ng current to the; alternate, contacts 48"and'58 of the relay 49', and upon ener ing' current W1 the rela. v 49,- h

station B only is responsive. Engagement'of actuating spring 50 'with contact 53' v be closed through locking relay 51 as follows: battery S, conductor 78,

causes circuit to conductor '52, relay 51, spring 50 and contact 0 ens the sleeve stran with the contact 55 'carries the mug gization of this relay this calltus' at the substation B.' Energizationo A 'weve r takes place only during'the timethat the segment 66 is; in con tact with conductor68"to' complete circuit from ground through 62 and segment 66, conductor 68-, contact69 and armature of relay '51, through relay 49, conductors 77 and 78 tenths-negative side ofbattery, the posi-' length than segm tive sidef-of the battery being grounded, as

shown.- Therelative'dimensions of the seg-.-

ments of 'thejint'errupters 59 and 56 are shownin Figs; '5 and 6; Groundedsgnient 66 of the interrupter 59 has a slightly greater ent. 64 connected with theenerat'or 46; and the interrupters travel together with the same shaft. .If'these seg-. mentswere of the same length, then when segment -66 connects conductor 68' -With oundto cause operation'ofrelay 49, which places the plu cords in the ringing'position,

oi the otheninterrupter will at the samemstant connect the ringing current to the line, and when segment'66 opens the segment 64 ground circuit toreleaserelay. 49 the ringing current would also be cut off by segr'nent 64. p

'Upon denergization of-relay '49-l-the tip strand: is cont nuedithrough armature -80 rand "cont'ac't81, through contacts 37 ;8 Il ,1-39,vW1n'ding 30.0 the superyisory relay. and'throfugh; conductors 86 and-8,4 to 'thejpositive grounds .and as:thesleeveside1 of the cord-circuit whenfof01in e"c tedwvitlrthe, t

line has alwaysconnection warding ed sidefofthe battery,

31 of the supervisory relayandtliitou h con} ductor 78 w-ithth'e negat vesidego'f t e battery, the entire charge whichthej condensers corresponding the segment 67 of :Engage- :the rin'gin l passinto the arm'atures 79 correspon ing and 80 to be extended to the signal appara-f 4 f and'the relay'de'ener the tip strand throng supervisoryrelay rto ground, The line and tent -c539 of the in the telephones and the lines have received will pass through the supervisory wind ng 30, and as this winding controls the contacts 33 and 34 included in thecircuit for relay 51, which in turn controls the circuit through relay 49, the signaling would be seriously lnterfercd with. It 1s, therefore,"'neces a maintain the actuation of relay 51 and relay 49 controlled thereby. a sufficient length of time to allow discharge of thehne'flthrough the ground connection for the signaling current interruptersand this'is accomplished by making the segment 66 slightly longer than segment '64, the exact operation of't'his arrangement being as follows: Suppose that the brushes for the interrupters' arerespectively at the be 64 Relay 49 ls energized and ringing cur rent at the same time 'appliedto-the cordconductors and connected line.

brush} leaves the section .64, section- 66 on account of its greater len th .After the .still connects with ground and maintains c 0-,

sureofthe' circuit for relay 49 and the charge retained in the condensers and line is led to roundedsegment 65 of After the grounded ground through the g current interrupter.

brush leavesthe segment 66 t ,e

ized to again complete the winding 30 of, the

other. circuits are thus entirely relieved of 'static' charges before and after application of ringing impulses thereto.

I The ringing 'cir 'Iming o'f-the sections 66 and circuit for relay 491s, opened cuit tosi nal' the subscriber'may be traced as ring 63 -and'segment 64-. to the key 45, through. contact 48 and armature 80 of'the .relay"49" to the tip-strandplu and sprin jack tot-he line limbathrough t e signa'l bel fat substation Bl. back to the-line limb b"! followisi om generator 46"'to interrupter the sleeve st-rand,

49 an through conductor '57 to the othef ten min'al of the generator 462 66' becomes disconnected from conductor 68 relay 49 becomes deenergized but on account of the adjustment-above described the lines- .wi-ll be free 'from'static charge} The length oi such periods of "current groundlng and interruption can articular conditions I 1 Upon receiving the signal the called sub,- his receiver and. closes the from: battery S through conductor Q78, winding- 3], conductor 86,

iteistraniplug 1 9 and engaged s I oughf the; linefan'd' substat on bac through ringjack and "plug .to the tip strand,

ithrougharmature 80,- through vsprlng 3 7 and v supervisory,relay/through another part of the sleeve "strand, through conductor r87,-winding 30, concluctor' 86"{and When segment be adjusted to suit the.

rmgjack engaged from the contact 34 to break the circuit through the supervisory lamp 40,

the looking relay 51 and this relay upon apparatus. "The subscribers are'now eon-- "tacts 25 and 26 and contacts- 33 and 34 to close the circuits through the supervisory the operator that conversation haslbeen spring 42 of the operators key, Before the a calling plug is inserted in the jack tne 'oper 'ator applies the tip thereof to the jack thimof the supervisory relay, throughconductor dependent for its efficiency ,upon the characthrough conductor 84 to theotherside of the battery. This causes the energization of the armature 32 and the spring33is disthus notifying the operator thatsubstation B- has answered. These contacts 33-and 34, however, were included in the circuit throughbreaking of said contacts becomes denergized to release the lockin plate 71, and con-. sequently' the actuated iey thus immediately causing actuation of theringing nected for telephonic conversation and upon completion of conversation thereceivers'. are replaced on their hooksto open the circuits through the windings'22 and 30 of the respective supervisory relays, thusallowing conlamps 29 and iO, respeet1vely,'t0 indicate to c1osed,wher eupon the operator removes the plugs to restore the apparatus to its normal condition. Y The "cord circuit may also be provided witha busy test arrangement controlled by; the: contacts 88'and 89 'associatedwith the ble and actuates. her listening key, If the" line IS' busy current will flow as follows; from negative battery through conductor sleeve contact to the engaged thimbl'e, to the tip of the applied testing plug tothe tip strand of the testing cord circuit, through armature '80 and contact 81 of the 'corre; sponding relay 49, through the contacts" 38 90, through engaging test contacts 88 and 89, through conductor 91,- through the test winding 92, through conductor 93' and through conductors 86 and 84 to the'positive side of battery, and the operator will be notified of the busy condition of the line.- If the line 'is not-busy this circuit Will not be'closc-d through the test winding and the operatorconneets'the calling plug-with the. jack of the line to be called and then pro-' ceeds as hereinbefore described. I 1

The relative arrangement between selective signaling apparatus andthe cord circuit, as herein. described, has been found to be very efficient andimuch, more .so than the arrangement heretofore used, in which" both signaling and controlling current 7 passed through acontrolling relay which was eel-- justed to respond only to. the direct current and which, consequently, was more or. less ter of thepdifferent currents.v I do not wish,

howeveigto be limited to the exact arrangement and relation. of the parts herein shown as changes may readily be made without departing from the spirit of my invention.

I claim. as new ters Patent;

and desire to'secure by Let- 1. In a telephone exchange system, the

combination'with a central exchange, of sub stations connected therewith through telephone lines, a cord circuit at the central exchange, a source of ringing current at the ce nrelay to connect the source with the cord cirwit and with a lineconnectedtherewith marily controlling the current flow from said source, a relay controlling the application-of ringing current to the cord strands, a second relay controlling the circuit through said first relay, actuation of the key causing closure of a circuit through said second relay, .and'in terrupte'r. means for the fi'rst relay circuit for causing interrupted application. of ringing current to the cord strands by thefiirst relay. I, 3. In a telephone exchange system, the combination with a, central exchange,- of 'a plurality of substations for connection there'- with through telephone lines, a cord circuit at the central exchange, a source of ringing current at the central exchange, a-key prima- 2. In 'a telephone exchange system, the" combination with a central exchange, of a plurality of subst ationsv forconnection there- -With through telephone lines, acord circuit at the central exchange, aisource of ringing ficurrent at the central exchange, a key pririly controlling the current flow from "said source, a relay controlling the applicationof ringing current to the cord strands, a second relay controlling the circuit t-hrough said first relay, actuationof the ,key causing closure of acircuit through said second relay, interrupternieans for the-first relay circuit for causing interrupted application of ringing .current to the cord stran (ls by the first relay,

and means for causing the cord circuit and connected line to be grmmded during a short interval before the application thereto of ringing currentl '4. In a telephone exchange system, the combination-with a central exchange, of a plurality of substations for connection therewith through telephone'lines, acord circuit at the central exchange, a source of ringing current at the central exchange, a key-primarily controlling the current flow from said source, a relay controlling thepapplication' of ringing current. to the cord strands, a second relay controlling the cireuit'through said first relay, actuation of thekey causing closureof a circuit through said second relay, interrupter means for the first relay circuit for I causing interrupted application of ringing current to the cord strands by the first re ay,

and means for causing the cord circuit and connected line to be grounded during a short interval before and after the application of ringing-current thereto. j5. Ina tele hone exchange system, the

combination wlth'a central exchange, of sub-- stations connected therewith through telephone lines, a cord'circuit at the central-exchangefor connecting substations together forconversation, a source of ringing current at the central exchange, a key forprimarily controlling the flow of current from said source, a relay directly controlling the application of the ringing current to the cord circuit strands, a second relay connected in circuit up'on actuation of the key, a circuit for the first relay controlled by said second relay, and interrupter means for interrupting the circuit through the first relay whereby pulsations of ringing current will be applied tothe cord circuit and line connected therewith,

said second relay being associated with saidk'ey tolock said key in its actuated position;

I 6. In a telephone exchange system,- the. combinationwith a central exchange, of substations connected therewith through telephone lines, a cord circuit at. the central exchange for connecting substations'together for conversation, a source of ringing-current at the central exchange, a key for primarily controlling the fiow of current from said cation of.'the-ringing current to the cor circuit strands, a second relay connected in circuit upon'actuation .oi' the key, a circuit for the first relay controlled by said second reinterruptermeans for interrupting the whereby "ulsource, a relay directly controlling the appli circuit through the first relay sations of ringing current will be a plie to, erewith,

tuated -key.

7.; In a telephone exchange system, the

combinatlon with a central exchange, of telephone lines leading therefrom and termin'atr' ing insubstationaacord circuit at thecentral exchange for connecting telephone lines together, a source of s1 naling current at the exchange, a ke primarily controlling the ci rcuit from said source,

trolling theiappliea'tion of ringing current to .the cord circuitfand line 'c'onne'cte controlling the circuit through a relay directlywcorh therewith, a second rela *said first relay and adapted ufpr said first relay, the circuit through said second relay being normally contro led by said key, said second relay being associated with said key to lock said key in its actuated position, and means upon actuation of substation apparatus in; answer to the signaling current ior. causing the circuit throu h said secondjrelay to be broken where y said key is released and the circuit through said first relay broken.

8. Ina tele hone system, the combination with a, centra exchange, of telephone lines leading therefrom and terminating in substations, a cord circuit at the central exchange for. connecting subscribers for con versation, a source of-ringing current at the central exchange, a, relay for controlling the connection of'said source 'with'the cord circuit," and a second relay for controlling thecircuit through said first relay, each of'said the cord circuit.

' 9."In a telephone exchange system, the

' combination with a centralexchangaof telephone lines leading therefrom and terminatingin substations, a cord circuit at the eeri tral'exchange, a source of ringing current at the exchange, a relay controllin the connection of'the sourcewith the cor circuit, and" a second relay controlling the circuit through on energization toclose circuit: throu the by said source "will" e st-relay' whereconnected with the relays directly controlling the continuity of I cord circuit each of said relays directly controllin the continuity'of the cord circuit.v 1 0. n a telephone exchange syste'm,'the combination with a. centralexchange, of substations connected therewith through telephone lines, a cord circuit at the central exchange, a source of rin ing current'at thecen tral exchange normal y disconnected from the cord circuit, a relay controllin the con- 'nection ofsaid source with the cor circuit, a

second rel'ay controlling. the circuit for said first relay,- and interrupter means in said circuit for periodically causing closure of said circuit to periodicallycause action of the first relay to connect the source with thecord circuit and with a line connected therewith, said relay'controlling the continuity of the clord circuit. I -11. In a telephone combination with ,a central stations connected therewith through telephone lines, I a cord "circuit and "a source of" ringlng current .at'the exchange, a sourcekof direct current at the exchange for supplying talking and signaling currents, 'a relay for controlling .theapplication of ringing current from said source to the cord circuit strands, a

exchangesystem, the 7 exchange, of subsecond 'relay. controlling the circuit through said first-relay, interrupter means for said -,'first relay; circuit f or perio dically interrupting the currenti fiowrtlieretlunug and interrupter means included in current I circuit adapted to alternately connect with ground and with the source. of signaling current, said interrupters acting in harmony whereby said first relay becomes inert.

ling the connection of the ringing circuit with the cord-strands, interrupter mechanismifor periodically .closingcircuit through saidq-re 5 lay whereby signaling current isperiodically said relay and adapted during one interval to closecircuit through the relay and at'ianl2. In atelephone exchangesystem, .the combinationfwith a central exchange, of tele-' phone lines leading therefrom and terminat ing in substations, a cord circuit" at the central exchange, a source ofsignaling current] at the central exchange, a" relay for .controlling the connection of the ringing circuit with the cord strands, interruptermechanism for 'periodically closing circuit through said relay whereby signaling current "is periodically ap plied to the cord circuitstrands, and means forgrounding the line-and cord circuit during a shortinterval before and after each applica fore and after receivingtcharges of ringing 'tion of ringing current thereto.

In a telephone XQha'nge system, the combination with a central exchange, f

phone lines leading-therefrom and terminating in substations, a cord circuit atjthecen tral exchange, a source of signalin g'current at the central exchange, 'a' relay for control applied tothe cord circuit strands, and inter rupter means associated with the ringing cir-'- cuit, said first and-second interrupter means acting in harmony and so adjusted that the cord circuitand li'neconne'cted therewithwill be grounded during a short interval immediately before and after the application of ringing current thereto. 1 14-. In a telephoneexcliange system, the

.combination wi'th a central-exchange, of tele:

phone lines leading therefrom and terminat ing; 1n substations, a cordc1rcu1't and a source of ringing current at the exchange, a relay controlling'the connection of the ringing cur: rent circuit'with the ringing cord strands, an interrupter controlling the circuit through other interval to open the circuit there? through, and an interrupter for theringing current circuit adapted during one-interval to connect with ground and during another interval to-connect with the source ofringing current, the length of the interval for apply-,

ing ringingcurrent by the one interrupter being less than the length of the interval of cloa short interval directly before and'after'the application of ringing current thereto.

minatingl'in substations, a cord circuit and a source of ringing-current at the exchange, a relay controlling the, application of the' ringing circuit totheline, to be called,fian' interrupter for controlling the circuit-through said relay, said circuit'being closed during part of the revolution of the interrupter and openedfduring the remaininglp'art ofthe revolution, and an interrupter for the ringing circuit adapted during part-0f its,'revolution'to connect'with ground and during the other part of its' revolution to connect. with the source of ringing current, the'interval of connection with the source offr'inging current being slightly less than the interval of closure of ,the relay circuit, whereby'theground con-- .nection will be maintained a: slight interval before and after application of ringing current and the connected line therefor grounded becurrent.

source of ringing current at the exchange, a

(source. of direct current at the exchange for supplying talking and signalingeurrents a relay. controlling ,the application-of ringing I circuit to the line'- to .be signaledyafsecond 4 relay controlling; the circuit ithroiigh said first relayrlthecircuit through'said firstrelay' being closed, upon closure of the circuit through said second relay whereby-thering ing circuit willbe-connected with'th'e line, a supervisory relay,- and switch ng means con-" trolled by the'supervisory relflyandactuated upon actuation ofsubstation -apparatus in' response to signaling currentatoopenthe cirf cuit through'said second relay whereb'y said I first relaybecomes inert and the-ringingcun ient circuit disconnected.

17. lnj'a telephone exchangelsystem,""thc combination; with a central exchange, of

telephoneline's leading therefrom and ter; 'min'ating in-substat1ons,- a cord circuit and.

a source of ringing current'at the exchange, a source of d1rec 't current at the exchange for supplying talking andsignali'ng currents,

a relay controlling the application of ringing current to ,theline to' be signaled, asecond relay controlling firstrelay,"a made relay for the cord circuit- I the "circuit through said closure, thecircuit through said second relay causing closure of the circuit through the first relay whereby said: first relay will be. energized to" connect the ringing" circuit with the line, a supervisory relay, and switching means controlled bygthe supervisory relay combination with'a central exchange, of telthe ringing current circuit and actuated upon actuation of substation apparatus in response to signaling current to open the circuit through said second relaywhereby said first relay disconnected, said relays jointly controlling the continuity of the cord circuit.

18. In a telephone exchange system, the

ephone lines leading therefrom and terminat-ing in substations, a cord circuit and a source of ringing current .atthe central exchange, exchange for providing talking and signaling current, a key primarily controlling the ringing circuit, a relay for directly controlling the application of the ringing circuit to the ringing cord circuit strands, a second relay control ling the circuit through said first relay, said second relay being. associated with said key to lock said key in its actuated position after actuation thereof, a supervisory relay, said second relay becoming energizedupon'application of the'key whereby the fi'rst relay' is energized to connect the ringing circuit with the cord strands and 'line'to be called,

and switching mechanism controlled by the supervisory-relay to open the circuit through the second relay upon actuation of substation apparatus in response to signalin'g'current, 'deenergizatlon of. said second relay 'causingdeenergization of the first relay and causing also release of the locked key.

19. In a telephone'exch'ange system, the combination with a central exchange, of telephone lines leading therefrom and ter minat ing in substations, a cord circuit and a source of ringing current at the centralexchange, a source of direct current at the exchange for providing talking and signaling current,- a re' lay for directly controlling the application of the ringing circuit to the ringing cord circuit strands, a second relay controlling the circuit through said first-relay, a key primarilycontrolling the circuit through said second relay, said second relay being associated with said key to lock said key in itslactuated position after actuation thereof, a supervisory relay,

said second relay becoming energized upon actuation of said key to closed circuitthrough the first relay whereby the first rela'y is energized to connect the rlnging circuit with the cord strands and dine to be called, and switching mechanism controlled by the supervisory relay to open the circuit through the second relay upon actuation of substation apparatus in response to signaling current,.deenergization of said second relayv causing denergiza tion of the first relay and'causing also release of the locked key, said relays jointly controlling the continuity of thecord circuit.

201 In a telephone exchange system, the combination'with a central exchange, of telehone lines leading'therefrom and terminating in substations, a cord circuit at the cenbecomes inert and a source of direct current at the tral exchange, a sourceof signaling current at the central exchange, a relay for controlling the connection of-the ringing circuit'withthe I cord strands, interrupter mechanism for riodically closing a circuit through said relhy whereby signaling.currentfisiperiodically ap lied to the cord strands, and'ine'ans for causing the line and circuits to'be relieved from charges before. and after each application of ringim current. c

-'-21. IIna telephone exchange system, the combination with acentral exchange, of telehone lines leading therefrom and terminating in'substatio'ns, a cord circuit. .at the cenaratus for the tral exchange, supervisory ap ing current at cord circuit, a source of signa the exchange, a calling'plug for the cord circuit, a relay for disconnecting the calling plug from the supervisory apparatus and for connecting said plug with the source of signaling current, means for interrupting the circuit I from said sourcewhereby pulsations of ringing current are applied to the line connected with the calling p V ing the line fromstatic charges after each pulfsation before said relayis restored to itsnor mal position to connect the calling plug with the supervisory apparatus.

22. In a telephone exchange system, the combination with a central exchange, of telehone lines leading therefrom and terminating in substations, a cord circuit at the central exchange, a source'of signaling current, indicating apparatus associated witjh'the cord circuit, a calling side of said cord circuit normally connected witlrthe indicating appara tus, a relay adapted upon actuation t'o disconnect the calling side of the cord circuit from the indicating apparatus and to connect said calling side with the source of signalingcurren-t, interrupter mechanism for causing alternate effective and ineffectivelperiods for the relay whereby the low of signaling cur:

rent is caused to be intermittent, and means for connecting the calling side of the cord circuit with ground after each application of ringing current before said relay becomes ineffectivewhereby the line and calling side of the cord circuit are relieved of static charges before the connection of the calling side with the indicating apparatus.

23. In a telephone exchange system, the combination with a central exchange, of telehone lines leading therefrom and terminating in'substations, a cord circuit at the central exchange, a source of signaling current at the exchange, a calling side for l3l18'.COI(l circuit normally connected with the remainder of the cord circuit, a relay adapted normally to cause connection of the calling side with the remainder of the cord circuit and adapted when actuated to connect said calling side with a source of signaling current, interruptcuit through said relay to cause actuation ugr, and means for reliev- 'tilne'that the first interruptingmeans is acthereof, additional interrupting mechanism for causing interruptions inthe flow of current from'said signaling-=, 'source said interrupting means being adjusted so that'cur rent will flow from said source duringthe tive, the active period of the first interrupt-g ing means being slightly prolonged for an interval beyond the period of current flow from said source, and means during such interval for connecting the calling side of the cord cir- 

